Question: Ashley is 14 years older than Christopher. Twenty years ago, Ashley was 3 times as old as Christopher. How old is Christopher now?
Explanation: We can use the given information to write down two equations that describe the ages of Ashley and Christopher. Let Ashley's current age be $a$ and Christopher's current age be $c$ The information in the first sentence can be expressed in the following equation: $a = c + 14$ Twenty years ago, Ashley was $a - 20$ years old, and Christopher was $c - 20$ years old. The information in the second sentence can be expressed in the following equation: $a - 20 = 3(c - 20)$ Now we have two independent equations, and we can solve for our two unknowns. Because we are looking for $c$ , it might be easiest to use our first equation for $a$ and substitute it into our second equation. Our first equation is: $a = c + 14$ . Substituting this into our second equation, we get the equation: $(c + 14)$ $-$ $20 = 3(c - 20)$ which combines the information about $c$ from both of our original equations. Simplifying both sides of this equation, we get: $c - 6 = 3 c - 60$ Solving for $c$ , we get: $2 c = 54$ $c = 27$.